Known sowing hearts for pneumatic single-grain sowing aggregates consist in general of two halves, namely a rear part, in which the mount of the sowing disk and the negative pressure area are installed, and a front part, into which the lower outlet of the seed container leads and which itself has a seed reservoir.
In sowing holes of the sowing disk matched to the size of the seed, which holes are arranged at specific intervals on a circle as a sowing hole series, individual grains of seed are removed from the seed reservoir and thrown off in a dispensing area by interrupting the negative pressure. If the interruption of the negative pressure is not sufficient to ensure dropping, an automatic wiper is provided at a short distance behind the ideal dropping spot. Per sowing disk, several sowing hole series can be arranged in circles of the sowing disk that are separated from one another.
In order to drop only one grain of seed if possible with each dropping, singulating devices are provided for each sowing hole series. In the case of a single seed, these devices work relatively reliably but hit their limits specifically in the case of tough seed, for example carrot seeds.